The present invention relates generally to portable power tools, and more particularly provides a unique vibration-damping control isolation system for use on portable rotary cutting tools such as flexible line trimmers, lawn edgers, or brush cutters, and other portable rotary power tools such as snow throwers, shaft mounted blowers and the like.
Portable rotary cutting tools of the type mentioned are typically provided with a small internal combustion engine or electric motor which is connected to and spaced apart from a rotationally driven cutting element by an elongated hollow shaft through which drive shaft means extend for transmitting rotational power from the engine or motor to the cutting element. Such tools are also typically provided with a rear support handle connected to the engine or the shaft, and a forward control handle secured to the shaft. During operation of the tool, the operator grasps these handles to enable him to support the tool and appropriately guide the rotary cutting element. In conventional power tools of this type, the forward control handle is rigidly connected to the shaft and projects generally laterally outwardly therefrom. During tool operation, transverse shaft vibration is transmitted outwardly through the control handle to the handgrip portion thereof which is actually grasped by the tool operator. As is well known, such vibration transmitted to the handgrip can render operation of the tool, especially when it is used for extended continuous periods, quite uncomfortable, often causing a numbing sensation in the operator's hand.
Various attempts have been previously made to isolate the handgrip portion in the forward control handle from this shaft vibration. For example, it has been a common practice to utilize resilient bushings to connect the handgrip portion to the balance of the forward control handle, or to use such resilient bushings at the connection point between the forward control handle and the shaft. However, these isolation techniques typically result in only a relatively small reduction in the shaft vibration ultimately transmitted to the handgrip.
Another proposed solution has been to provide the forward control handle with an open-looped configuration in which one of the loop ends is rigidly connected to the shaft, with the other loop end being free so that the handgrip portion defines a generally central section of the open loop. This control handle configuration renders the overall handle somewhat more flexible, thereby providing a slight additional reduction in the shaft vibration transmitted to the operator handgrip.
However, each of these conventional control handle designs, in common with other conventional handle designs, still often transmit an undesirably high amount of shaft vibration to the operator handgrip.
It is accordingly an object of the present invention to provide an improved shaft-mounted control handle which will more substantially diminish shaft vibration transmitted to its handgrip portion.